I saw seven bills passed since he first joined the House of Representatives in 1991, two of which were postal facility renamings. And though https://www.govtrack.us/congress/members/bernard_sanders/400357 says that passing only 7 bills since 1991 is not ineffective, realize that's less than one every three years for the past 29 years.
Also on that list: declare #VT bicentennial day. If one is considering "effectiveness", the post office renaming laws and the bicentennial day law probably should not be counted. That's four in 29 years. We should divide the effectiveness ranking into Bernard Sanders' time in the House and Bernard Sanders' time in the Senate. We'd have to compare others after doing the same sort of pruning to see whether he's actually as ineffective as this appears.