The answer to your question really depends on the quality and frequency of the service offered by your school and whether that matches a particular child's needs. I suspect that many schools discourage taking kids out because they want to protect their own attendance records and stats. In the case of my child, who is non-verbal at 4 yrs old, I asked and the school discouraged taking her out. I'll be taking her out anyway, however, because this is the greatest area of need for my child and the school doesn't have a PROMPT trained SLP. In your case, perhaps you could ask the school to come in one day to observe the quality of OT your child is getting, then compare that with what a private OT can offer before you decide?