Two contrasting mouth coloring pages for your student to grasp the difference in articulation/mouth part placement, if your student produces an S with their tongue between their teeth, thus, actually producing a Th sound instead.
I like to begin speech articulation therapy with these coloring pages, so student can color while listening to my lesson on tongue placement, mouth position and air flow, and while they practice correct placement, and repeating the sound in isolation.
Once we move on to syllable or word position, I like to keep their coloring page displayed so I can point to the part of the mouth they need to focus on and correct.
They can also take the S sheet home to hang up as a reminder to practice, thus facilitating generalization of the sound.
I also display the whole mouth collection above the white board, so students can easily visualize that our mouths look different for all sounds, while they wait for their turn in group.
Also, I always have folders of these "Mouths" on hand for any new student or new sound a student might need, or for comparison between sounds.