I would suggest that you request that the school evaluate him to see why he is having such issues. I am not discoraging you from helping him, but if you do all the work, they have no idea what he needs, and his needs may soon overwhelm your ablity to both help him and provide services and pay for them yourself. The school is obligated to eduate him. Find out why his grades are bad, he does not have to fail to get help. It sounds to me like this is in the learning disablity category, but it may not be. While sylvan has a place, it should not be the first line attack. I would suggest two things, first, make an appointment with a Neuropsychologist and get an educational evaluation so that you know exactly what your son needs, and second, write to the school and request an evaluation because he is stuggling in (blank) then list all the areas he had difficulty with. There should be a meeting to discuss what evaluations will be done, and frankly, it probably should have happend already if his grades are like they are, and the school should have initiated it.
Once you have both, you can supplement what ever he does not get from the school so that he gets everything he needs. That way, you are getting him all you can, and the school takes the first role in his education. It will probably work better that way, and you will not have so much frustration and keeping up to do with his work.
I have not been seeing too much "spontanious" RTI from schools. Unfortunately, it usually takes the parent writing a letter requesting evaluation, which is expensive, to make a district follow the 3 tiered process for RTI. RTI is perfered by IDEA, but not required. It certainly does make sense, and it would be great if it were done, but what I am seeing is districts hidigng behind RTI as a defense for why they are not doing anything about the kids who struggel, or why one of them missed being identified. Theoretically, a child who is not picking up on learning in any area, should be started with the first teir of RTI as soon as in class interventions are unsucessful, without parents needed it make any request, but that is not what is happening. Kids are still struggling in classrooms wtih typical instruction and are not being refered for evaluation, nor placed in RTI, and parents like K. are finding themselves exactly where parents have always found themselves, struggling to provide so that their child is a success and not hearing from the school first, being forced to sound the alarm alone. I wish it were different. RTI would be a great alternative so that so many kids were never identified as LD, and ended up making progresss, but from where I sit as an advocate, parents still have to make the first move to get RTI, and they must still go forward and make the formal written request for an evaluation, and if there is RTI to be had, they might get it. It is sad, but I am not sure most parents want RTI once the child gets to the point where they have to make the request, it is just about too late for that once parents figure out how to navigate the system. Very sad.