Further Maths A Level Edexcel optionWatch
Despite having an M.Sc. in Computer Science, and 20 years extremely successful software development behind me, I always advise students not to choose Decision Maths as an option. There is only one reason I advise this, It's because with all the writing and drawing even very good students often run out of time, so it's very hard to get top marks in these options.
Maybe the school isn't one of the bad ones. One hallmark of a bad school/teacher is that student are forced to do Decision Maths. Another is when students are force to take the medical physics option.
Most schools don't have the funding to give students options on which modules they teach. Most schools offer exactly the number of modules required in the exam and don't waste their time teaching excess content. That doesn't make a school worse than a private with the funding to offer more choices. Even most private schools near me don't offer students the choice.
If you really want that extra module for whatever reason, maybe have a look at Further Pure 1?
I'm not saying schools should teach several at the same time. However, as the students have to take the exam the class should vote on the option. In bad schools incompetent teachers force their choice on the class because they don't feel up to teaching anything else.
In an ideal world, sure. But I've never seen a school that does this because it's simply unfeasible and teachers can best provide support for modules they know and understand best. It's unfair to categorise all schools which don't take this approach as bad- plenty don't do this and get excellent results.