Is the YMCA an educational institution within the purview of Article XIV, Section 4, par. 3 of the Constitution?

No. The term "educational institution" or "institution of learning" has acquired a well-known technical meaning. 

Under the Education Act of 1982, such term refers to schools.  The school system is synonymous with formal education, which "refers to the hierarchically structured and chronologically graded learnings organized and provided by the formal school system and for which certification is required in order for the learner to progress through the grades or move to the higher levels." The Court has examined the "Amended Articles of Incorporation" and "By-Laws" of the YMCA, but found nothing in them that even hints that it is a school or an educational institution. 

Furthermore, under the Education Act of 1982, even non-formal education is understood to be school-based and "private auspices such as foundations and civic-spirited organizations" are ruled out. It is settled that the term "educational institution," when used in laws granting tax exemptions, refers to a ". . . school seminary, college or educational establishment . . . ." Therefore, the private respondent cannot be deemed one of the educational institutions covered by the constitutional provision under consideration.