The Sentence Diagram Generator visually represents the sentence "My students are really excited for the ACT test" as follows:

                +---------------------+
                |        are          |
                +---------------------+
                |                     |
          +-----+-----+             +---------------------+
          |           |             |        excited      |
          |           |             +---------------------+
          |           |                     |
      +---+---+   +---+---+           +-----+-----+
      |   My  |   | really |           |     for    |
      +-------+   +-------+           +-------------+
      |           |                     |
 +----+----+  +----+----+         +----+----+
 | students |  |  ACT    |         |  test   |
 +----------+  +---------+         +---------+

This diagram illustrates the subject ("My students"), the linking verb ("are"), the predicate adjective ("excited"), and the prepositional phrase ("for the ACT test").