I think it sounds about as good as you're likely to get for that time of the year.
To give you an idea of what you're looking at, the BA sale fare (always a good benchmark) which is available at the moment for the time you're travelling is just under £320 including taxes midweek, £15 more each way for weekends.
One other thing to watch out for is that it sounds like you're flying back in school half term week. Availability of the cheapest fares is always poor that week for obvious reasons. A play with the Fare Explorer on BA's website will demonstrate what I'm talking about.
In short, if that's when you need to travel, I'd go for it at those prices.