Summer Mandarin Immersion Abroad for High Schoolers

My son is a junior in high school and he currently takes Mandarin. He’s actually quite good at it and would like to spend a few weeks in China improving his proficiency this summer. He applied for the NSLIY program and was not accepted, so we’re looking for another program he could do. The cost is not really an issue, but I’m struggling because there are just SO MANY programs out there, and it’s hard to tell which is a good one. There’s a neat looking school called LTL through which he could do a homestay. There’s also this place in Shanghai called RISH (Real in Shanghai) which would include staying with a group on campus. Does anyone have any recommendations? He emphasizes that he really wants to focus on improving his Mandarin, not really volunteer work, etc. I just want something reputable and dependable. He’s a good kid but he’s just 17 and I want a program that I feel is safe.

We hosted an exchange student through Youth for Understanding. I thought it was a very good program…they had orientations for the students and parents and had the students check in with someone from YFU to make sure all was okay.
https://www.yfuusa.org/study-china