In England, judging has not been confined to the professionals. Ordinary people play a key role - and many people regard that as an important protection for liberty. Without their involvement justice would be administered solely by State Officials.
The two key areas involving non-State employees are
(1) in Magistrates Courts, where the norm is to have a bench of three lay magistrates hearing trials of summary offences (and who also may hear "triable either way" cases). All criminal cases start in Magistrates Courts - though indictable cases, and those "triable either way" where it is felt more appropriate to be heard in the Crown Court (a defendant may demand his right to a jury trial) - begin (usually only briefly) in the Magistrates Courts.
(2) in Crown Courts, where the decision on whether the defendant is found guilty or non-guilty, is given to a jury.
It is useful to be able to outline the qualifications/disqualifications for being a lay magistrate or a member of the jury. But it is just as, if not more, important to be able to discuss the advantages and disadvantages of each type of lay involvement.
In previous posts I have included MindMaps - can I invite you to prepare your own MindMaps with the key points for each side of the argument. Do add pictures - and if you scan them in and send them to me , I will seek to publish them in a later post. This post from 2009 may be of some use to you.