Cortisol response to the TSST, measured as Area Under the Curve, increase from baseline. 7 Samples were taken during the course of the assessment, at (1) arrival for training purposes; (2) after the calming video, 30 minutes after arrival; (3) after 5 minutes of speech preparation; (4) after 10+minutes of speech and math performance; (5) 15 minutes after sample 4; (6) 10 minutes after sample 5; (7) 10 minutes after sample 6. Area under the curve at intercept (AUCi) is calculated using samples 2-7 with sample 2 as the intercept.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Salivary Alpha Amylase response to the TSST, measured as Area Under the Curve, increase from baseline. 7 Samples were taken during the course of the assessment, at (1) arrival for training purposes; (2) after the calming video, 30 minutes after arrival; (3) after 5 minutes of speech preparation; (4) after 10+minutes of speech and math performance; (5) 15 minutes after sample 4; (6) 10 minutes after sample 5; (7) 10 minutes after sample 6. Of those, samples (2, 4, 5) are assayed for salivary alpha amylase (sAA) in micrograms per milliliter. Area under the curve at intercept (AUCi) is calculated using samples 2, 4, 5 with sample 2 as the intercept.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Self-report of stress using a Likert-type scale with 5 levels of stress felt: (1) Not At All, (2) A Little, (3) Some, (4) A Lot, (5) A Whole Lot. Level of stress was reported for at these points during the assessment: (1) How stressed did you feel when you first connected on the video call and saw the experimenter?, (2) How stressful was the period of time before we started the video?, (3) How stressful did you feel while watching the video?, (4) How stressful was the period of time when you were preparing your speech and thinking about what to say?, (5) How stressful was giving the speech?, (6) How stressful was the math portion?, (7) How stressed do you feel now, after the speech and math portions are done? Self reported stress was computed as the mean of items (4, 5, 6) - item 1.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Participants report the number of hours between waking up on the day of assessment and the start of the TSST test.

This is only a potential covariate for cortisol, which follows a circadian rhythm.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Parents report on gross family income on an 11-point ordinal scale: (1) Less than $15,000, (2) $15,001 to $25,000, (3) $25,001 to $35,000, (4) $35,001 to $50,000, (5) $50,001 to $75,000, (6) $75,001 to $100,000, (7) $100,001 to $125,000, (8) $125,001 to $150,000, (9) $150,001 to $175,000, (10) $175,001 to 200,000, (11) $200,001 or more

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Parents report education level for both parents on a 6-point ordinal scale: (1) Less than high school degree, (2) High school or GED, (3) Associate degree, college academia program, (4) Bachelor's degree, (5) Master's degree, (6) Professional and/or Doctorate degree. Average of parents' education is calculated and reported.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Parents report on how many adults are living in the home.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Youth report on whether they consumed caffeine or nicotine in the 1-2 hours prior to the TSST assessment. Coded as no=0, yes=1. Used as a potential covariate for heart rate and neuroendocrine measures.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

The Granger score (ordinal, modeled continuously) is a score based on work by Doug Granger of medications that can affect activity of the HPA axis, weighted by significance of potential impact (Granger, Hibel, Fortunato, & Kapelewski, 2009). Each medication taken is given a score of 0, 1, or 2, and all medication scores for a participant is summed, resulting in scores from 0 to infinity. Lower scores are less likely to influence cortisol. Potential Covariate

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Network of Relationships Inventory (NRI) reported by youth for their primary parent on how much they experience various emotions or incidents (e.g. How much free time do you spend with this person?), reported on a 5-point scale: (1) Little or None, (2) Somewhat, (3) Very Much, (4) Extremely Much, (5) The Most. Mean scores calculated from all positive attachment items, range 1-5. Potential Covariate. This self report reflects the general current state of the relationship, without a specific timeframe, and was obtained during the TSST session.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Network of Relationships Inventory (NRI) reported by youth for their close friend on how much they experience various emotions or incidents (e.g. How much free time do you spend with this person?), reported on a 5-point scale: (1) Little or None, (2) Somewhat, (3) Very Much, (4) Extremely Much, (5) The Most. Mean scores calculated from all positive attachment items, ranging 1-5. Potential Covariate. This self report reflects the general current state of the relationship, without a specific timeframe, and was obtained during the TSST session.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Scale on the MacArthur Health and Behavior Questionnaire, 5pt scale (1-5), high scores indicate peer acceptance. This report reflects the general current state of the youth, without a specific timeframe, and was obtained during the TSST session.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Scale on the MacArthur Health and Behavior Questionnaire, 3pt scale (0,1,2), high scores indicate inhibition. This report reflects the general current state of the youth, without a specific timeframe, and was obtained during the TSST session.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Higher order measure from the MacArthur Health and Behavior Questionnaire, 3pt scale (0,1,2), high scores indicate Internalizing. This report reflects the general current state of the youth, without a specific timeframe, and was obtained during the TSST session.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.

Higher order measure from the MacArthur Health and Behavior Questionnaire, 3pt scale (0,1,2), high scores indicate externalizing. This report reflects the general current state of the youth, without a specific timeframe, and was obtained during the TSST session.

256 participants were completed, with 61 Friend and Target Both, 65 Friend Support, 62 Unfamiliar Peer, and 68 Alone. For each outcomes, all available analyzable data were included in results, sometimes resulting in lower n.