There is extensive literature regarding speech in children with cleft palate. Our team constantly monitors early production of speech both in terms of intent as well as quality. The speech pathologists are present during each cleft clinic visit and their input is a critical part of the team evaluation. We have a more formal protocol beginning at ~ 18 months and again at ~ 2 years of age. I think this is a similar approach taken by most of the cleft teams in the country. I would refer to speech literature for a more accurate and detailed answer.
In her thesis (Kristina Klintö at Karolinska Institutet, Sweden, 2014) my colleague has explored speech materials for speech evaluation in children with CLP. Her conclusion is that "Word naming, in combination with sentence repetition, is recommended for evaluation of cleft palate speech when best performance and performance in coherent speech are assessed." We start with monitoring babbling at 10 and 18 month, then follow ups at 3,5,7,10,16 and 19 years of age as agreed upon nationally at all 6 centers in Sweden using the same speech materials and protocols to evaluate speech parameters such as nasality - velofaryngeal function, articulation and intelligibility.
May I recommend the textbook Cleft Palate Speech by Howard & Lohmander to you? You will find more answers there!
Our openion for patients with cleft palate that it is a team work cases. Language and speech evlauation must be done as early as possible after surgical intervention which is the main factor affecting speech output as if it is done by clever surgeon leading to adequate palatal length and mobility the speech out put expected to be very good and if short and immobile palate the patient well need a hard work to slightly improve his speech
evaluation can be done subjectively by direct or indirect way by lestening to and examination of the patient by expiernced Phoniatrician or SLP