Agreement of past participle

Question

In a recent Kwizbot about the article with days of the week/weekend, an example was given « Ce weekend, on est allés au Futuroscope ». Why is the past particle plural?  « We » is implied but the subject is « on ».

Maarten Kamp · Accepted Answer

Patricia, 
I know this question has been asked and answered here previously but can’t find a link presently. 
The verb associated with ‘ on ‘ always conjugates in 3rd person singular, but there is a more complicated ‘ rule ‘ of agreement of past participles and adjectives ( that not even all French speakers know ).
The attached to the Laura Lawless site discusses the nuances of agreement of adjectives and past participles following ‘ on ‘. 
Regardless of the other uses, when replacing the subject pronoun ‘ nous ‘, with ‘ on ‘, there will usually be agreement in number/gender following ‘ on ‘ ( just as there would have been with nous in Kwiziq material ), as that is the usual approach on this site.
https://www.lawlessfrench.com/grammar/subject-pronoun-on/

Patricia Currie · Answer

Thank you. I understand that it is more a personal choice but in learning situation, check opinon of teacher.

Cécile Janty-Davies · Answer

Just to add to what Maarten has said, Patricia, please take a look at the following lesson, which explains the different uses of the subject pronoun on -
On can mean either we/one/people (French Subject Pronouns)