For many parents with disabled children in public school systems, the lure of the private school voucher is strong. Vouchers for special needs students have been endorsed by the Trump administration, and they are often heavily promoted by state education departments and by private schools, which rely on them for tuition dollars. So for families that feel as if they are sinking amid academic struggles and behavioral meltdowns, they may seem like a life raft. And often they are. But there’s a catch.