I think you can make your own goal attainment scale, where you can varie with the heigth, length of, and distance between the objects. I do not recall a scale which measures just that.
Stepping over obstacles to improve walking in individuals with poststroke hemiplegia
David L. Jaffe, MS; David A. Brown, PhD, PT; Cheryl D. Pierson-Carey, MS, PT; Ellie L. Buckley, MS, PT; Henry L. Lew, MD, PhD
Rehabilitation Research and Development Center, Department of Veterans Affairs (VA) Palo Alto Health Care System, Palo Alto, CA; Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL; The Permanente Medical Group, Inc., Fremont, CA; Cornell University, Ithaca, NY; Stanford University School of Medicine, Palo Alto, CA
Obstacle Test
Obstacle clearance performance was measured as subjects attempted to step over foam obstacles ranging from 2 x 2 in. to a height and length determined by their leg length. Maximum obstacle height was equal to the height to the subjects' inferior border of the patella while maximum length was height to the subjects' trochanter minus one-half the maximum obstacle height. Subjects were given three chances to clear each obstacle without touching it or circumducting it. The longest obstacle successfully negotiated at each height was recorded.