What is the ruling on praying Asr individually after missing the congregational prayer due to studying in high school, given the absence of a prayer area and the prohibition of leaving the lesson?

Congregational prayer is obligatory and is not waived except for a legitimate excuse. If it is possible to combine attending the lesson with congregational prayer, then that is religiously incumbent. If that is not possible, then attend the lesson and then pray in congregation. You should be a caller to goodness everywhere, especially in school.