Our experience is very like CFK's. Good intentions, failure of teachers to monitor or keep up with DS's progress, resulting in a near-complete lack of instruction. DS got less than a third of a year of math across a year of school, and nothing that was appropriately challenging.
In our state, this situation is actually illegal; all kids who are enrolled are required to have math instruction every day. Because of this we were able to set up a better situation for next year.
A kid this age, it seems to me, needs a teacher's attention and instruction to learn this material; they don't yet have the self-discipline to guide their own learning, even if they're motivated. I haven't found the computer programs to be a good substitute.
I think kids vary a lot, especially these kids: but I doubt mine has the self-discipline to work at hard things in a sustatined way without some teacher input. Ah well. His teachers last year and the year before were both, in their different ways, excellent for him, so I shall just have to hope that this year's teacher is too. I'll certainly be updating on how this year goes, and hope you will too!
