As an example, I found seats at this price on Iberia departing Boston BOS on Wednesday, April 15, with a return flight from Madrid MAD on Friday, April 24, 2020. Overlapping on April vacation for most schools.
Departures at this price are available starting on September 30 through the end of booking calendar in May. Peak holiday dates in December and early January blacked out.
Travel from the U.S. is valid Sundays through Wednesdays, with returns from Madrid open on Tuesdays through Fridays. A minimum stay of 7-nights is required.
This Basic Economy fare includes a carry-on bag plus one personal item. A checked bag costs $60 each way.
Seats will be assigned at random upon check-in for this price.
Main Cabin Economy fares are available for $414 roundtrip, which includes one free checked bag, advanced seat assignments, and allows ticket changes/upgrades for a fee.
Boston fare details and booking info.
New York fare details and booking info.