How does the author use foreshadowing in When You Reach Me?

All the notes and clues that Miranda gets foreshadows a discovery. Consider:

You will want proof.
3 p.m. today: Colin's knapsack.
Christmas Day: Tesser well.
April 27th: Studio TV-15

Miranda ends up finding something in Colin's bag that even he could not have know would be there when he arrived at school that day.