"attended at" is a correct and usable phrase in written English
You can use it when referring to attending a specific event or place. For example, "He attended at the school's graduation ceremony."
Regular attendance was defined as having attended at least 80% of the last 20 school days.
Antenatal care attendance was categorized as having attended at least one visit or none.
He attended at the same time that his grandchildren were in university.
The suspect attended at least one of Ms. Giffords's town meetings before the event Saturday.
This was the most impressively formal occasion the writer attended at the Konigsbergs.
It was he who had attended at the scene of the accident.
To report the features of cancer patients attended at a hospital Emergency Department.
20 We also investigated children of parents who attended at least some college.
Of 190 patients; 101 (53.2%) attended at least one follow-up visit.
10,000 or so people have attended at least one of them.
Here's a panel I attended at the recent Pacific Crest Technology Leadership Forum in Vail, Colorado.
