If I already hold a valid certificate to teach in the public schools, may I teach in preschool? A If I already hold a valid certificate to teach in the public schools, may I teach in preschool? Not necessarily. If your certificate to teach is a Pre K-2nd Grade Certificate, you may then be certifiable through the Massachusetts Department of Early Education and Care. If you hold a certificate for grade 3 or higher, then you would most likely have to take courses related directly to young children.