Which is a vertical goal attack strategy?

• A. Treat /k/ and /f/ simultaneously until 70% correct; then treat /ʃ/ and /ɹ/ simultaneously until 70% correct.
• B. Treat velar fronting in /k,ɡ,ŋ/ simultaneously until the process is observed less than 20% of the time.
• C. Treat /s/ until 90% correct; then treat /z/ until 90% correct.
• D. Treat /s/ until 90% correct; then treat /ʒ/ until 90% correct.

Answer: (C)

Vertical goal attack focuses on one target sound at a time until a high level of accuracy is reached, then moves on to the next sound. The sequence described—treat /s/ until 90% correct, then treat /z/ until 90% correct—fits this approach clearly: you establish a precise target, work it to criterion, and only then switch to another distinct sound. This explicit, one-at-a-time progression is the essence of vertical therapy.

The other options mix targets within the same phase or treat multiple sounds or processes simultaneously, which aligns more with horizontal or cyclical approaches, where several targets are practiced together or revisited over time rather than mastered individually before moving on.