I have attended two of Sara's workshops. I have a 7-11 year old student with a frontal lisp who still sucks his thumb at night and sometimes during the day. His tongue is forward with an open mouth position when he is at rest. I haven't yet checked to see if his swallow is affected. Should I wait until he has stopped sucking his thumb before I start tongue retraction exercises and using the straw, horn and blowing procedures? (I intend to give the parents suggestions to encourage him to stop sucking his thumb. I have Marshalla's, How to Stop Thumbsucking and Mayer & Browns', My Thumb & I.)
You obviously understand the relationship between thumb sucking and the frontal lisp, but...remember kids sometimes have prolonged tongue sucking because they are seeking stimulation to the temporo-mandibular joint (TMJ). This child sucks his thumb at night, so he may be using it to calm down and relax his body to go to sleep. The sucking during the day may be related to frustration or to calming when he is relaxing or tired. I would certainly look at when he is sucking to see if it is pure habit or if it is based upon jaw weakness, asymmetry or stress. If any of these issues are present, then a behavioral approach to eliminate the thumb sucking would not be indicated. Taking his thumb away could result in the formation of other habits to address the need (sucking on his tongue, biting his nails, grinding his teeth).
I delve into this extensively in my book Assessment and Treatment of the Jaw: Putting it all together - Sensory, Feeding and Speech. If there is a muscle-based component to his frontal lisp, then using a behavioral approach alone will not be effective. With that said, I use Pam's book myself and think it is a great asset to eliminating the tongue sucking WHILE doing the OPT interventions.
Your first step is to do an assessment of his jaw, lips and tongue using the Bite Blocks, Straws and Horns to see if there is a muscle- based component. If so, you may be interested in looking at my most recent book OPT for /s/ and /z/. I use a combination of OPT and traditional speech therapy techniques, including auditory discrimination and training, in addition to production activities, to normalize the muscle skills needed for standard production of the /s/ and /z/ up to the conversational level.
I hope this helps, but if not please feel free to email me again.