The control will be an inactive condition of standard care at the time of the intervention. 'Standard care' may include access to Parent Schools in Mother and Child Health clinics at public hospitals, which are provided in some provinces and districts in Thailand.

Child maltreatment (physical and emotional abuse) will also be measured through the Home Observation for Measurement of the Environment (HOME) Inventory - Abusive and Harsh sub-scale. The original HOME Early Childhood and Middle Childhood Inventory Forms will be discussed and finalized by the Parenting Experts Working Group during the formative evaluation. The Abusive and Harsh sub-scale is expected to contain six items that utilize dichotomous scoring, with two items assessed via interview in the home regarding whether the parent used physical punishment or yelled at the child during the past week, and four items assessed via observation regarding whether the parent scolded or yelled; used physical restraint; hit, slapped, spanked, or kicked; and pushed, pulled, or pinched the child during the home visit.

Child maltreatment: physical & emotional abuse (self-report)

Physical abuse (including abusive discipline) and emotional abuse will be measured using 20 items from an adapted and expanded version of the International Society for the Prevention of Child Abuse and Neglect (ISPCAN) Child Abuse Screening Tool-Trial Caregiver version (ICAST-T). The ICAST-T measures parental reports of the incidence of abuse perpetrated against their child over the past month using a frequency score on a scale of 0 to 7, or 8 or more times (e.g., "In the past 4 weeks, how often did you discipline [Child Nickname] by pushing, grabbing, or kicking him/her?"). This study will assess overall indication of previous child abuse (0 = no abuse; 1 = previous abuse), and frequency of overall abuse by summing all of the subscales.

Positive parenting behaviours will be assessed using the Parenting Young Children Scale (PARYC) (21 items), which measures the frequency of positive parenting (7 items), setting limits (7 items) and proactive parenting (7 items) by the parent/primary caregiver over the previous month on a 7-point Likert scale (0 = Never, 6 = Always). Items are summed to create total frequency scores for each subscale.

Dysfunctional parenting behavior will be assessed using the Arnold Parenting Overreactivity subscale (PS, 10 items), which examines parent attitudes and beliefs regarding authoritarian discipline. PS responses are based on a 7-point Likert scale in which parents are presented with a situation and then are given two opposing responses at either side of the scale, with the mid-point representing neither one way or the other and the three points on either side of the mid-point representing "sometimes," "generally," and "very often" as one moves further out from the middle. One such item under this subscale is "When my child misbehaves, I raise my voice or yell…I speak to my child calmly." (7 = I raise my voice or yell; 1 = I speak to my child calmly.) Scoring for this subscale is computed by averaging the responses on these items.

Parental monitoring and supervision practices will be measured using an adapted version of the Alabama Parenting Questionnaire (APQ) Poor Monitoring/Supervision subscale (11 items). The APQ measures parenting characteristics that have been associated with disruptive behaviour disorders in school-age children, although it has also been used with preschool children. The Poor Monitoring/Supervision subscale will be used to measure the frequency of negative parent monitoring and supervision practices over the past month through a 5-point Likert scale (0 = Never; 5 = Always). Items include "Does (the target child) stay out later than he/she is supposed to?" and "Is (the target child) left at home without adult supervision?" The items in the scale are summed to obtain a total scale score.

Child neglect will be assessed using an adapted version of the ICAST-T Caregiver tool (mentioned above) Neglect subscale. This subscale has 6 items for assessing medical, physical, and educational neglect, including "In the past month, how often was [Child Nickname] not taken care of when sick or injured, even when you or another caregiver were able to do so and could afford it?" and "In the past month, how often was [Child Nickname] not given a meal that he or she needed, even when you or another caregiver was able to afford it?"

Parental depression, anxiety, and stress will be assessed through the Depression, Anxiety, and Stress Scale short form (DASS-21) (21 items) . The DASS-21 will assess parent/primary caregiver depression and anxiety using a 4-point Likert scale [0= Never; 3 = Always] to measure the frequency of symptoms over the previous week. Items include statements such as "I felt that I had nothing to look forward to." Total DASS scores range from 0 to 63, with subscales from 0 to 21. The recommended cut-offs that indicate severity of depression are 5-6 (mild), 7-10 (moderate), 11-13 (severe), and 14 and up (extremely severe), while cut-offs for anxiety are 4-5 (mild), 6-7 (moderate), 8-9 (severe), and 10 and up (extremely severe). Cut-offs for stress are 8-9 (mild), 10-12 (moderate), 13-16 for (severe), and 17 and up (extremely severe).

For the purpose of assessing child behaviour problems by parent/primary caregiver self-report, the study will utilize the Eyberg Child Behaviour Inventory (ECBI) Intensity Scale and Problem Scale (36 items). The Intensity Scale measures the frequency of child externalizing behaviours over the past month, using a 7-point Likert-like scale (1 = Never occurs; 7 = Always occurs). Both scales are summed to create a total Intensity Score and Problem Score, with clinical cut-off scores for disruptive behaviour problems suggested as 131 for the Intensity Score and 15 for the Problem Score in the USA. However, no Thai norms are available.

Attitudes toward punishment will be assessed using one item from the UNICEF Multiple Indicator Cluster Survey (MICS) 5 Child Discipline module. The MICS item asks the parent/primary caregiver: "In order to bring up, raise up, or educate a child properly, the child needs to be physically punished." Parents/primary caregivers will report whether they disagree or agree with the statement based on a 5-point Likert scale of 0 to 4 (0 = Disagree strongly; 4 = Agree strongly).

An adapted version of the Parent Daily Report Checklist (PDR, 44 items) will be used to assess day-to-day occurrences of child behaviour problems and parenting behaviour. In order to assess child behaviour, the PDR asks parents/primary caregivers whether a child externalizing behaviour (e.g. destructiveness, lying, hitting others) occurred within the previous 24 hours (34 items), as well as how much sleep the child had (1 item). To assess parenting behaviour, the PDR asks parents about their own behaviour (6 items, e.g. yelled or shouted at the child, praised child for doing something well) and self-efficacy (3 items, e.g. had a feeling that I could not cope with parenting). Responses to these items are dichotomous (0 = No; 1 = Yes), with items summed for each subscale on parent and child behaviour. The item regarding sleep is a numerical response.

Parent-child relationships will be measured through a combination of interview and observational items (27 in total), using a combined and adapted version of the Early Childhood and Middle Childhood HOME Inventory record forms, as aforementioned. The HOME Inventory is scored dichotomously. The adapted version contains 16 items on the "responsivity" sub-scale; 6 relevant items on the "encouragement of maturity" sub-scale; 2 items on the "emotional climate" sub-scale; and 2 items on the "modelling" sub-scale.

Adult self-report of experiencing intimate partner violence over the past month will be assessed using an adapted version of the Revised Conflict Tactics Scale Short Form (CTS2S, 6 items). This scale includes 2 items on the frequency of negotiation (e.g., "partner suggested a compromise for a disagreement"), 5 items on physical assault (e.g., "partner pushed, shoved, or slapped me"), and 1 item on psychological aggression (e.g., "partner insulted, shouted, yelled, or swore at me"). Answers are coded on a frequency scale of 0 to 3 (0 = never happened; 1 = once or twice; 2 = 3-5 times; 3 = More than 5 times). The CTS2S will determine an overall indication of intimate partner violence on a level of severity (sum of items) and prevalence (dichotomous variable indicating experience of conflict or not), as well as for each subscale.

Adult report of ICAST-T Attitudes subscale (4 items). These items concern a hypothetical scenario of a child with behavioral problems, and parents report whether different disciplinary methods (e.g., "hitting or spanking the child") were effective or ineffective according to a 5-point Likert scale. Items are summed.

Parent sense of inefficacy will be assessed using an adapted version of the ICAST-Trial Inefficacy Subscale (2 items, e.g., "In the past month, how often did you not know what to do when your child misbehaved?") The items are summed for a total score ranging from 0 to 16 with higher scores indicating a greater sense of inefficacy in managing difficult child behaviour.

Adult report of partner coercion based on the WHO questionnaire on women's health and life events (10 items) (Garcia-Moreno, Jansen, Ellsberg, Heise, & Watts, 2005). The WHO assesses experiences of partner coercion (e.g., "partner took your earnings or savings from you against your will"). Responses are scored on a frequency scale of 0-8, with items for each instrument summed to obtain a total score, as well as a score for the negotiation subscale.

Adult report of Intimate partner violence (IPV) negotiation (2 items; e.g., "partner suggested a compromise for a disagreement"). Items are summed.

Quality of delivery will be assessed by coaches observing the delivery of programme sessions six and seven (two sessions per facilitator) using the Parenting for Lifelong Health Facilitator Assessment Tool (PLH-FAT). The PLH-FAT, similar to the Leader Observation Tool for the Incredible Years parenting programme, is an observational treatment fidelity tool used to assess the process skills necessary for delivery of the programme. It will examine whether and to what extent core intervention components have been delivered, including questions regarding topics touched on per session, such as home practice discussion and role-playing activities. Seven standard behaviour categories are grouped into two scales based on the core activities (23 items) and process skills (28 items) as outlined in the programme manual.

For the purpose of measuring adherence and exposure to the parenting programme, attendance registers will be kept for each weekly session in order to assess the level of exposure of participants to the intervention components.

Participant engagement in home activities will be measured through weekly participant self-reports of home activity completion, using parent home practice checklists (Appendix H). Participants will complete the forms on a daily basis following the first seven weekly sessions, and these will be collected by facilitators at the beginning of sessions two through eight and maintained in participant case profiles. The forms will indicate to what extent the participants were able to practice the home activities assigned during the previous week's session and in accordance with the intervention manual.

Quantitative data on participant satisfaction will be assessed through a satisfaction questionnaire (45 items) that will be administered to post-intervention, adapted from questionnaires used to evaluate PLH for Young Children programmes during RCTs in South Africa and the Philippines.

Quantitative data concerning participant engagement and programme acceptability will also be assessed through participant case profiles, which are maintained by facilitators on a weekly basis and will contain notes regarding how individual participants react or engage with the programme material.

Qualitative data on facilitator and coach satisfaction/acceptability of the programme will be gathered via a focus group discussion with all facilitators and coaches following programme conclusion.

Data will also be captured through facilitator session reports and coaching reports. Facilitator session reports will include descriptions of their positive and negative experiences in delivering the programme material. Coaching reports will consist of information from weekly coaching sessions on their coaching experiences, including approaches or issues that worked particularly well or challenging areas that required further attention.

During the feasibility pilot, obstacles to programme engagement for participants will be assessed using the Obstacles to Engagement Scale (OES) (15 items). The OES measures the influence of personal and intervention-based obstacles to attending the parenting programme sessions. The scales asks parents/primary caregivers to rate each item on a 4-point scale (1=Definitely no; 4 = Definitely yes), with four sub-scales measuring personal or family stressors and obstacles (4 items), relevance of and trust in the intervention (4 items), intervention demands (4 items), and time and scheduling demands (2 items).

Qualitative data will be gathered through in-depth interviews with 12 parents/primary caregivers, conducted following programme completion. The Interviews will be conducted according to an interview guide, with five broad questions that explore issues of participant satisfaction and perceptions of acceptability according to the themes of: overall programme experience, learning and practicing parenting skills, programme delivery methods, scheduling, and logistics.

Additional information concerning participant perceptions of engagement and programme acceptability will also be assessed through participant case profiles, which are maintained by facilitators on a weekly basis and will contain notes regarding how individual participants react or engage with the programme material.