Classes assigned to this condition received the mindfulness-based intervention. The MBI program implemented comprised ten weekly sessions. Activities were drawn from the Mission Méditation program, a MBI intervention specifically tailored for elementary school children. Activities comprised in this intervention encompassed formal (e.g., body scan, sitting, and breathing meditation) and informal meditations (e.g., mindful eating, listening, and touching, mindful walking), as well as positive psychology exercises (e.g., taking care of oneself, gratitude). The weekly sessions, lasting 45 to 60 minutes each, were delivered in a group format by the teachers themselves, in their classroom.

Placed on waitlist and then offered the intervention once the data collection phase was over.

The MBI program implemented comprised ten weekly sessions. Please refer to the arm/group descriptions for further details.

Children completed selected items from the self-report version of the anxiety (three items, e.g., "I worry about little things"), depression (five items, e.g., "Nothing ever goes right for me") and inattention (4 items, e.g., " I forget to do things") subscales of the Behavior Assessment Scale for Children (BASC II)

Participants rated how competent, autonomous, and related they felt in school, by answering a nine-item scale adapted from a scale used in a previous, similar study [57]. Children were asked to rate their agreement with items such as "In school, I feel free to be myself" (autonomy); "I am able to reach my goals" (competence) and "In my relationship with others, I feel appreciated" (relatedness) on a 5-point Likert scale ranging from 1 (almost never) to 5 (almost always).

Finally, participants completed the Mindful Attention and Awareness Scale for Children (e.g., "I find it hard to stay focused on what's happening in the present moment."; [58]) to evaluate pre-to-post changes in their mindfulness abilities. They rated their agreement with each item on a 6-point Likert scale ranging from 1 (never) to 6 (almost always). A higher score on this scale indicates lower levels of mindfulness.