Speech-language pathologists (SLPs) frequently assess children's speech to diagnose and identify areas of difficulty, then determine appropriate intervention goals. Formal measures are available for assessment; however, many SLPs use informal measures within clinical practice. The purpose of this two-part mixed methods study was to describe informal measures created to assess children's speech. Study 1 involved a systematic review of 39 informal measures identified via journal database and internet searches, scanning of reference lists, and submission by SLPs and researchers. The measures were reviewed in terms of their conceptualization (content and format) and operationalization (evaluation and validation). Common conceptual features included assessment of consonant singletons, single words, computer format, and picture-naming. Few measures provided information addressing operational criteria; in particular, they lacked evaluation of their effectiveness. Study 2 involved an inductive thematic analysis of journal entries from eight creators of informal measures that explored key considerations in the development process. Informal measures were created due to the absence of measures which were sufficiently comprehensive and culturally appropriate, plus a desire to incorporate technology. Considerations in the creation of informal measures included sourcing research and existing measures to inform the measures' development, maximizing children's engagement, and utility. SLPs must be cautious when using informal measures due to their lack of operationalization. However, these measures often address SLPs' needs and so operationalization of informal measures would be beneficial for the profession.