I believe it is because "fait" doesn't exist as "faite" or "faites", It appears to be immutable.. Apparently only the PP that end on é are matched in number and gender, as in: "Anne s'est douchée". I am not a native speaker, though. -- Chris.

Merci. I think I have found the answer - " In certain expressions, such as faire + infinitive, laisser +infinitive, se rendre compte, and others, the place of the direct object is held by an infinitive or other complement, which will always follow the principal verb. In these expressions no agreement is usually made".

Merci In the example "la tarte que j'ai faite est delicieuse" the past participle in this case agrees with the noun (la tarte - the object of the sentence) (even though it is an avoir, not etre, construction) because it PRECEDES the participle. On the other hand "J'ai fait la tarte does not agree because la tarte (the object )comes after the participle. Merci Laura and Claus. Laura please can you explain the causative construction, which i'm sure is a better way of explaining this grammar point?