Sacks’ claim (normalized) is that roughly a year of COVID-era school closures may cause learning loss and social isolation whose negative effects persist across an entire generation of affected students, i.e., for decades.

What we know by late 2025:

• Severe and persistent learning loss is well documented. Global analyses by the World Bank, UNESCO, and UNICEF estimate that this cohort of students stands to lose around $17 trillion in lifetime earnings, warning that learning losses from COVID-19 school closures could “impoverish a whole generation” of students. These estimates project long-run income and productivity losses over their working lives, not just short-term setbacks. (unesco.org)
• Long-run economic and social impacts are explicitly expected to last for decades. World Bank work on learning loss projects that school disruptions have permanently reduced learning-adjusted years of schooling for the current cohort and will lower their lifetime earnings; recent summaries state that these learning losses can translate into lower productivity, greater inequality, and increased risk of social unrest “for decades to come,” unless aggressively remediated. (blogs.worldbank.org)
• Educational recovery has been slow, not complete. In the U.S., 2024 NAEP assessments show high school seniors’ math and reading scores at their worst levels in roughly two decades, with large shares of students below basic proficiency, and experts noting that the pandemic exacerbated an already downward trend rather than being fully reversed by 2024–25. Five years after the initial disruptions, many students remain significantly behind pre‑pandemic benchmarks. (apnews.com)
• Youth mental health and development show sustained harm. Studies and surveillance data indicate marked increases in anxiety, depression, suicidal thoughts, and other mental health problems among adolescents associated with pandemic isolation and disruption. Some research links post‑shutdown adolescents to worse mental health and signs of accelerated or stress‑like brain aging relative to pre‑pandemic peers, and CDC data show substantial burdens of poor mental health and suicidal behavior tied to pandemic‑era adverse experiences. (nimh.nih.gov)
• Five years of follow‑up is still far short of a “generational” timescale. Some longitudinal and follow‑up work finds that many adolescents are still experiencing elevated mental health problems and functional difficulties about five years after the first lockdowns, suggesting multi‑year consequences but not yet documenting outcomes across their full adulthood. (dw.com)

Putting this together:

• The evidence already strongly supports multi‑year, potentially lifetime impacts on learning and earnings for the cohort exposed to prolonged school closures, and it shows sustained mental health consequences. These findings make Sacks’ warning about a possible “generational consequence” plausible and well‑grounded.
• However, the core of the prediction is about decades‑long, generation‑wide outcomes (e.g., actual lifetime earnings, adult health, social stability). As of 2025, the affected students have only advanced a few school grades; their full working lives and long‑term adult outcomes have not yet unfolded.

Because the crucial part of the claim concerns effects spanning an entire generation over decades, and we are only about four to five years past the closures, the prediction cannot yet be definitively judged as right or wrong. The best characterization is “too early to tell,” even though current data point strongly in the direction he feared.