The schools in many areas around Wareham have just changes from 3 tier (first, middle, upper) to 2 tier (primary, secondary).
There is a brand new primary school in sandford just outside Wareham that feeds into Lytchett minster school which is good.
Poole & bournemouth are separate LEAs from dorset, and have different school systems completely- some 3 tier, but poole mostly becoming 2 tier. The grammar schools start in year 7, and are more difficult to get into if you're not within the poole catchment.
I've not heard of anyone having trouble getting secondary places, but I haven't got kids of quite that age yet!
Wareham is lovely, if a bit sleepy small townish. The road from Wareham to everywhere else is gridlock on hot sunny days because it's the main route to all the beaches in the purbecks.
It depends on where you'd like to live- you can choose busy town, sleepy towns, suburbs, country villages, small hamlets. All are close enough to Wareham.
We live west of poole, fairly rural & DH commutes to bournemouth easily.