Hey goosey, I accept the point, but it is no good providing sources that are a mere half a dozen years out of date!Mr Pedant here. It's still the Easter Holidays for many schools around the area, including LEA schools in Birmingham (only the second week).
School term dates | Birmingham City Council
School Year 2017 to 2018 Spring Term 2018 Term Starts: Monday 8 January 2018 Half Term: Monday 19 February 2018 to Friday 23 February 2018 Term Ends: Thursday 29 March 2018www.birmingham.gov.uk
They haven't sold out. They aren't selling entry, which is your entire premise.
They are fully booked out, with free entry, for two weekdays of the Easter holiday.
I pity those who pay £10.00 for The Wave, with its recent operating throughput. I would not want to be the 283rd person in that queue.
Drayton is a park that would make far more money if there was a cheap entry/tickets option on a regular basis, even if only off peak.