If you are planning on becoming a RCM, then you will have to go on an ICP course supplied by your local council and it is during one these sessions that you get your CRB check lesson.
Be as honest as you can be. Do not assume it is spent, it isn't for an enhanced check, and just explain exactly what happened at the time of the offence, any fine or sentence you received and how the assault actually came to happen
I have to say though, that I don't rate your chances to highly on being passed by OFSTED who will have the say so in whether they will register you, or not and not your local council.
Best of luck
ojx