Change in parental reflective functioning as measured by parent/caregiver report on the Parental Reflective Functioning Questionnaire. Responses are reported on a 7-point Likert scale from 1 to 7. Total scores for the three sub-scales (Pre-Mentalizing Modes, Certainty about Mental States, and Interest and Curiosity) range from 6 to 42. Lower scores on Pre-Mentalizing Modes, moderate scores on Certainty about Mental States, and higher scores on Interest and Curiosity indicate better outcomes..

Change in parental positive feelings about having a gender diverse child will be measured by administration of a caregiver self-report using the Trans Youth Can! Parent Positive Feelings Checklist (TYC-PPFC). Each item that is endorsed by the respondent as having occurred is scored as '1'. If the caregiver endorses 'something else', each incident mentioned that is not already captured in existing checklist items is scored an additional '1'. The sum total of the endorsed items is the final score for this measure. Higher overall scores are indicative of more positive feelings parents/caregivers of trans and non-binary youth experience in regard to their youth's gender.

Change in parental worries about having a gender diverse child will be measured by administration of a caregiver self-report using the Trans Youth Can! Parent Positive Feelings Checklist (TYC-PWC). Each item that is endorsed by the respondent as having occurred is scored as '1' (excluding the 'I have no great concerns' option which is coded as '0' and must be a unique choice if selected). If the caregiver endorses 'something else', each incident mentioned that is not already captured in existing checklist items is scored an additional '1'. The sum total of the endorsed items is the final score for this measure. Higher overall scores are associated with more potential factors that may concern parents/caregivers of trans and non-binary youth with regard to the youth's gender.

Change in perceived interpersonal support will be measured by administration of a caregiver self-report using the Multidimensional Scale of Perceived Social Support (MSPSS). The MSPSS is a 12-item scale designed to measure perceived social support from three sources: Family, Friends, and a Significant Other. All items are scored on a 7-point Likert scale, from 1 (Very Strongly disagree) to 7 (Very Strongly agree). Higher overall scores are associated with caregivers who perceive to receive greater interpersonal support from their social network.

Intervention acceptability will be measured by Acceptability of Intervention Measure (AIM). The AIM is a 4-item subscale that measures the extent to which a new treatment or innovation is found to be acceptable by the caregiver within this setting. All items are scored on a 5-point Likert scale, from 1 (Completely disagree) to 5 (Completely agree). Higher scores correlate with greater acceptability of the intervention.

Intervention appropriateness will be measured by Intervention Appropriateness Measure (IAM). The IAM is a 4-item subscale that measures the extent to which a new treatment or innovation is deemed to be appropriate by the caregiver within this setting. All items are scored on a 5-point Likert scale, from 1 (Completely disagree) to 5 (Completely agree). Higher scores correlate with greater appropriateness of the intervention.

Change in therapeutic group cohesiveness will be assessed using the self-reported Cohesiveness subscale of the Therapeutic Factors Inventory (TFI-COH). The Therapeutic Factors Inventory is a larger battery with 11 different subscales, developed to measure the therapeutic factors in group psychotherapy. The TFI-COH subscale used in the current study specifically assesses participant experiences of bondedness, acceptance, and mutual liking and trust within a particular therapy group. The TFI-COH includes nine items rated on a 7-point Likert scale ranging from "strongly disagree" (1) to "strongly agree" (7). Two items are reverse scored and then summed with remaining items to yield total scores ranging from 9 to 63. Higher total scores are generally indicative of perceptions of greater (more positive) cohesiveness within the therapy group.

Changes in therapeutic process variables will also be assessed using the using the Working Alliance Inventory - Short Form Revised (WAI-SR) scale. The WAI-SR is a 12-item patient-rated questionnaire that measures three domains of therapeutic alliance: agreement between patient and therapist on the goals of the treatment (Goal); agreement between patient and therapist about the tasks to achieve these goals (Task); and the quality of the bond between the patient and therapist (Bond). All items are scored on a 5-point Likert scale ranging from 1 ('rarely' or 'never') to 5 ('always'). Higher scores indicate a better therapeutic alliance.