You can't refer to the calculated values later in the select statement like you are in the ROUND() function. You would have to use the AVG() function again in there like:
SELECT oxadmain.name , oxadmain.year , oxadmain.photoID , oxadmain.thumbs , stuperfdaily.ID , stuperfdaily.stuid , stuperfdaily.date , stuperfdaily.subject , stuperfdaily.teacher , stuperfdaily.cw , stuperfdaily.hw , stuperfdaily.con , stuperfdaily.par , stuperfdaily.att, AVG(cw) as cwAverage, AVG(hw) as hwAverage, AVG(con) as conAverage, AVG(par) as parAverage, AVG(att) as attAverage, ROUND((AVG(cw)+AVG(hw)+AVG(con)+AVG(par)+AVG(att))/5, 2) AS avg FROM stuperfdaily INNER JOIN oxadmain ON stuperfdaily.stuid=oxadmain.stuid GROUP BY stuperfdaily.stuid
ORDER BY oxadmain.stuid ASC