Many school records are held at PRONI and the dates covered vary greatly. To see if the records do exist you need to know where the family were living and then check the schools in the area.
County Derry records (not complete) show a Laurence Margy born 1854 (probably from a baptism) & a Laurence in 1880. Several Patricks- 1879 (more than 1?), 1883, 1884, 1885.
Only marriage for a Lawrence Margey is 1906 to Rose Bradley.
Patrick Margey m.1879 Co. Derry to Ellen McKendry. (exact date and place not listed on index). If this is the correct couple then it is highly likely that Patrick was born too early for existing school records but it is always worth looking.
School registers will give date of entrance, name of child and age (later date of birth), religion, residence (townland), father's occupation- names of parents are NOT given.