Start it like /t/ — tongue up on the ridge — then let it go into sh. Two sounds glued into one: ch.
Check yourself: Say /t/ then shhh, faster and faster, until they join.
Watch for: sh. A child who says 'shair' for 'chair' is missing the /t/ at the front.
◆ marks a word that does NOT follow today's pattern — Blumenfeld boxes these on the page. Teach it by heart; do not let the class sound it out and lose faith in the rule.
Say the word, have them repeat it, count the sounds on fingers, THEN write. The count is what stops a child writing the first letter and guessing the rest.