Tags are in approximate order from main to less major elements.
Nazo no Kanojo X (Mysterious Girlfriend X)
Romance, School life
Shounen, Comedy, Delinquents, School Life, Romance and possibly Love Triangle (though kind of implied in Shounen)
Orange Yane no Chiisana Ie
Seinen, Romance, Comedy, possibly Slice of Life.
Comedy, 4-Koma, Romance, School life, Slice of Life