The COVID-19 pandemic has altered the family dynamics of most people worldwide as well as the mode in which students take classes. The impact of such changes on students' well-being, academic engagement, and general distress remains unknown. Therefore, this study aims to test the structural relations among positive family environment (a measure of Positive Home-Based Parent Involvement [HBI]), subjective well-being (SWB), general distress, and academic engagement, focusing on Mexican high school students. A longitudinal study was conducted covering two time points: before (T1) and during (T2) the COVID-19 outbreak. A sample of 502 students answered questionnaires in T1 whereas 111 did so in T2. Analyses were conducted using Mplus software. Principal results showed that the positive and significant association between positive family environment and SWB did not substantially change from T1 to T2, whereas the relation between positive family environment and academic engagement became stronger. Data revealed that a positive family environment can play an important role in promoting academic engagement among adolescent students despite the risks brought about by sanitary lockdowns and the increase of family interactions. Results are discussed highlighting the importance of positive family environments and HBI on academic outcomes for Mexican high school students.