Think about the different aspects of school - directors, administration and students and liken them to the different tasks undertaken by each part of the cell.
This could be canteen, art or science supply store, office with student files - any area whose main purpose is storage.
Centrioles (groups of microtubules): 'temporary scaffolding'
This is a bit harder to come up with a 'physical' analogy. But what about gossip. Student talk about an interesting topic spreads very quickly through the school - just like the replication of centrioles. Another analogy might be flu - again spreading through the school very quickly. However, unlike flu, centrioles are not harmful.
Chloroplasts: Photosynthesis - energy provider
Solar panels on roof of school (remember though that chloroplasts aren't really located on the 'roof' of cells). The analogy could also accept the cafeteria as the chloroplast - providing the energy for the students and staff.