if you want to get all records where the name is one of the three, Mark, John or Kate then 'OR' is what you use.
In criteria in a query under your name field enter
Mark or John or Kate
The above assumes of course that your name field just contains the pupils first name. If it includes 2nd initial and/or surname then you should set criteria of
mark* or john* or kate*
Access will automatically fill in 'like' before each of the names.
If you just want Totals for each of the names then do a Totals query, put in the name field twice, put the criteria under one and set to 'Count' in the totals row. This would then give results of
Example:
Mark 10
John 25
Kate 8
If you want a result of 43 then need to set 'Where' in the totals row.