I am sorry to learn of this situation.
Is there a reason why his teachers were not advised of his IEP?
Part of the purpose of an IEP is to advise the student's teachers (in addition to the administration) of any specific needs or additional concerns that need to be addressed in the classroom. It is difficult to claim that an IEP is not being addressed or implemented if the student's teachers are unaware of its existence.
If the administration/school is at fault for not bringing the teachers into the IEP process earlier in the year, they should be remedying this promptly.
You can of course consider a private education - but if you want the school district to pay for it, you are going to have to go through the IEP process (give the school an opportunity to implement an IEP with his teachers aware of the plan, and address problems) first.
Make sure that you are communicating with the school in writing throughout the year - if problems come up, send a note (it does not have to be a lengthy letter, but a quick note or email to the teacher, special education coordinator, or administrator best positioned to address the problem (or copying any combination of these) will help ensure that there are open avenues of communication, preserve records of your efforts, and hopfully help improve your child's learning experience).