The certified is actually certificated - indicates they had obtained a certificate of competancy (I assume from England)
Re parochial schools - try www.manxnotebook.com/history/educ/1847.htm for some details but there is a very detailed history of Manx Education available (Hinton Bird) but he doesn't devote too much time to the grisly details of the generally poor parochial schools) - post the education act of 1872 things improve - an account by Sneyd-Kynnersly is at www.manxnotebook.com/fulltext/hmi.htm

There would only be the one teacher (possibly with an assistant and maybe one other for the very young pupils) - look at www.manxnotebook.com/cd_only/mate/p061.htm - the building in centre was the I believe the old dame school in Sulby - Jurby probably looked fairly similar (the walls still stand near Jurby church)