Hopefully their interest expands beyond single syllable words, otherwise the highest scores according to a cursory search are 'zizzed' (34) and 'jazzed' (32) which are probably slightly below the average for an elite player.
Of course most good players will create more than 1 word per turn, and will lay down over multiplier tiles.
You can probably do fairly well with just single syllable words, although at a certain level not being able to get a lay down bonus will prevent you from winning.
9 SCRATCHED
9 SCREECHED
9 SCROUNGED
9 SCRUNCHED
9 SQUELCHED
9 STRAIGHTS
9 STRENGTHS
9 STRETCHED
The CMU dictionary thinks that "scrambled" is two syllables as a vowel ends up between the "b" and the "l" in pronunciation. Wiktionary thinks this is a syllabic l (/l̩/), which should probably be counted as a separate syllable even if it isn't considered a vowel.
Wikipedia says
> Many dialects of English may use syllabic consonants in words such as even [ˈiːvn̩], awful [ˈɔːfɫ̩] and rhythm [ˈɹɪðm̩], which English dictionaries' respelling systems usually treat as realizations of underlying sequences of schwa and a consonant (for example, /ˈiːvən/).
That's consistent with what the CMU dictionary is doing, perhaps treating /l̩/ as /əl/.