The thrashing started as early as the second minute when Chris Shuker sped down the right and delivered a low cross to the far post were winger Martin Devaney coolly side-footed home.
It was 2-0 on seven minutes when Jacob Burns delivered an in-swinging free-kick which was firmly headed home by full-back Bobby Hassell.
Barnsley could have had a further three goals in the next 15 minutes as Scunthorpe's defence was ripped apart - particularly by former player Paul Hayes.
And Hayes played his part in the third goal which arrived just after the half-hour mark.
The striker showed tremendous awareness to slide a pass across the box for strike partner Marc Richards to finish in style.
Barnsley also had the edge in the second half and Hayes once more played his part when he crossed for Shuker to make it 4-0 in the 71st minute.
Scunthorpe's best player, 40-year-old winger Peter Beagrie, grabbed his 100th career goal from the penalty spot in the 89th minute but just seconds later the same player then saw his mis-placed pass fall nicely into the path of Hayes who clinically finished to make it 5-1.
Scunthorpe did manage a second consolation goal in stoppage time through Neil McKenzie.