NFPA 101 states that any door within a fire/smoke partition must be rated for the partition and must positively close. A classroom door is within a fire/smoke partition if the door is rated as a fire/smoke door (the door will have a metal tag on the hinge side of the door providing the door’s fire/smoke rating) and has a mechanical closer installed.
If this is the case, then Life Safety Code requires that the door freely close. At no time is the door allowed to be “propped” open. This includes a magnetic strip that restricts the door from latching.
In the event of a fire, air movement is a key component to the restriction or conflagration of a fire. A magnetic strip that restricts the door from latching allows the door to open due to the difference in temperature between the spaces in which the door penetrates.
A fire will seek the path of least resistance, which, scientifically, is moving from an area with high temperature to an area with low temperature. The effect of a high-temperature area combined with a low-temperature area creates a suction effect between the two areas. If the door between the two areas is not latched, this effect will open the door, allowing the fire to promulgate from one area to another.
If the door using the magnetic strip isn’t part of a fire/smoke partition, then the code does not have any requirements.