Unfortunately, those schools’ students are being exposed to this generation’s many negative influences. This is certainly food for thought. While the lack of secular education may be appalling to you, you must realize that secular education may not be an important goal for the community you are referring to. (I do not know which community you are describing, as I am unfamiliar with communities in the U.S. that do not offer secular learning in high school.)
The reason I cannot hold a view on charedi schools not supplying its children with a secular education, despite my strong support for its teaching (and your seeming support for it, as well), is because these are not my children and, as such, I have no say as to how they are educated or not educated. However, as this is a group within our community with which you interact, you might be able to find ways to make a difference, at the very least for the students with whom you work.
I was struck by the negative tone in your letter and can only hope that none of that negativity comes across in your relationship with your students and the administration of the school. Focusing on the positive ideas and achievements of those with whom you work can make a difference in how your ideas are received.
Thank you for expressing your concern and for wanting Klal Yisrael to succeed here in the U.S. Perhaps your letter will bring positive changes to the schools you refer to. Finally, your help to struggling students is incredible. Hopefully, that assistance will make them better functioning members of society. Hatzlachah!