How many times does Ravenbloom Student get the effect from a single cast of Icathian Rain?

Ravenbloom Student will get its effect once from a single cast of Icathian Rain.

According to Rule 383.3, when a condition for a triggered ability is met, it is placed on the chain. Ravenbloom Student's ability triggers "When you play a spell." Regardless of how many targets or instructions a single spell like Icathian Rain has, it is still only played once.

As clarified by RiftJudge FAQ #10004 and the general mechanics for "When you play a spell" triggers:

1. You play Icathian Rain (it enters the chain).
2. The "When you play a spell" condition is met, placing the Ravenbloom Student's triggered ability on the chain.
3. Because Icathian Rain is only played once, the trigger condition is only met once.

The multiple "Deal 2" instructions within Icathian Rain are part of that single spell's resolution, not separate spells being played, so they do not cause the Student's ability to trigger again.