Phonological and Other Speech Disorders

Phonological Disorder: Patterns of sound errors known as Phonological Processes (see chart below for a list of common Phonological Processes), are deviations from the rules governing how sounds fit together to make words. Use of phonological processes within speech can often simplify or significantly reduce a child's speech intelligibility.   The following chart is a great source that I reference often for phonological processes and the age at which most children discontinue using the processes. 
(click image for link to chart) 
This chart was created by Katie Yeh, MA CCC-SLP 2011 using the following references: 
Bowen, Caroline, (1998). Typical speech development: A gradual acquisition of the speech sound system. Retrieved from http://speech-language- (9-25-2011).
Shipley, K.G. & McAfee, J.G.,(1998). Assessment in speech-language pathology: A resource manual (2nd edition). San Diego, CA: Singular Publishing Group.
Hegde, M.N., (2001). Pocket Guide to Assessment in Speech-Language Pathology (2nd edition). San Diego, CA: Singular Publishing Group.

Apraxia and Other Motor Speech Disorders:
 Apraxia is characterized by difficulty with the motor planning necessary for speech production. It is considered an oral motor planning disorder.  Apraxia is not related or caused by weakness of the articulatory/facial muscles.  True oral motor weakness is characterized by weak articulatory muscles (lips, tongue, cheeks). 
Apraxia vs. Speech Delay
Additional Differential Diagnosis for Apraxia

A great source for Apraxia:

Phonological? Apraxia? Articulation? A great resource comparing Speech Disorders, by