Exercise 3: Adding Windows to a Running Session From Outside — Possible Solution
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Make sure the session exists (and is detached):

  $ screen -dmS work             # creates it detached, if it doesn't exist
  $ screen -ls

Add the two windows without attaching:

  $ screen -S work -X screen -t monitor htop
  $ screen -S work -X screen -t disk watch df -h

(Use top instead of htop if htop isn't installed.)

Attach and check:

  $ screen -r work
  Ctrl-a "

The window list shows, for example:

  0  bash
  1  monitor
  2  disk

Switch to windows 1 and 2 to see htop and the disk usage refreshing.

WHY THIS WORKS AS AN ANSWER
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It uses -X to send screen's own "screen" command to the session, which
opens a new window, and -t to give each window a clear title. The
window list is the proof they were created without attaching. Note
that each window closes if its command exits.