certificate of enrollment; certificate of school registration
An official document issued by a school confirming that a student is currently enrolled.
I had the university issue a certificate of enrollment.
Similar meaning; 在学証明書 is also a certificate of enrollment, but 在籍証明書 may be used more broadly for being on a register, not necessarily attending classes.
Compound of 在籍 (being on a register) + 証明書 (certificate).