Hi there, we are Upper Clapton, just on the north side of Millfields Park. Southwold School is very rapidly improving under new leadership (my DD1 is there, I have been very impressed), Harrington Hill is also very nice, partic early years but didn't get such a good Ofsted recently. I have also looked at Millfields school (really nice, good Ofsted but big - 3 form intake) and Baden Powell on the other side of the Lea Bridge roundabout (again, really liked it).
The streets around the Chatsworth Rd in Lower Clapton / Homerton are getting much much nicer than they were and I think the schools that side will improve accordingly by the time your son is school age. I don't know the schools there as it's not quite our catchment. Chatsworth Rd itself has got much more chic even in the 3 years we have been here, there are delis, good coffee shops, a kids bookshop and toyshop, I hear restaurants and bars etc popping up too (not that I get out much these days!) and the market on a Sunday is really lovely. Clapton Hart pub on the roundabout is fab.
One of the other reasons we love it is that the marshes / Lea Valley Park are just at the bottom of the road, real big open space for the kids, nature reserves, walks along the river, a riding centre and ice rink too.
I can't say it's a 'nice' area yet and if you really want a Crouch End type place then Clapton will be a disappointment. It's not there yet, but it's on its way and you might get a bargain.
(I get so torn between a) wanting more people to discover Clapton and b) wanting it to stay a bit undiscovered!)