Thank you for using the Jiskha Homework Help Forum. You are absolutely correct! You are working with "agreement of the past participle in the passé composé."
1. Past Participles conjugated with "avoir" agree in gender and number with the preceding direct object. (if there is one) This is what you are working with here. "les devoirs" as the direct object in "Je les ai faits" is masculine plural and the past participle illustrates that.
2. Past Participles conjugated with "être" agree in gender and number with the subject. Leur chèvre est morte. = Their goat is dead.
Past Participles of reflexive verbs agree in gender and number with the preceding direct object (if there is one). Elle s'est brossée = She brushed herself. BUT Elle s'est brossé les cheveux = She brushed her hair.
caution: no agreement with "parler" which takes an Indirect Object = nous nous sommes parlé = reflexive = we spoke TO eachother (ourselves).
Hopefully that clarifies that?