I’m not sure what is covered in Spanish in your son’s high school, but my Spanish classes seem to follow the standards here fairly closely - https://www.nationalspanishexam.org/index.php/exam-content/exam-specifications/. The grammar for level 2 seems to be go at a much faster pace than level 1. I’m not sure how helpful it would be to repeat level 1, when he is planning on taking level 2 anyways. It might even be a good idea to plan to repeat level 2. I took up to AP Spanish (5th year Spanish at my high school), and Spanish 2 was by far my most difficult class. Looking back, I think this was mostly because I had to adjust from the pace of Spanish 1.