The centre-back, 19, joins the Posh from the Premier League side Birimigham City after impressing their manager Darren Ferguson during a similar loan at the Iron last season.
Craig Morgan and Gabriel Zakuani are set to begin the season as the first-choice defensive partnership at London Road, but Ferguson hopes Pearce can provide competition for places at the back.
"He has good mobility and good pace, is young and wants to learn," Ferguson told the BBC.
"He's quick and powerful and, in my opinion, is a very good signing for the club."
Pearce is not short of first-team experience after enjoying loan spells at Notts County and Port Vale before heading to Glanford Park last summer.