It bears all the hallmarks of Verrocchio's studio, from the direction of the head to the use of white heightening to add detail and a feeling of depth. It does, though, use far more heightening than Verrocchio has used in his other drawings, of those still in existence.
The curls of hair are perhaps the most memorable item to this portrait, beautifully put together in a format that would have been particularly time consuming. Many of this artist's drawings were handed around his studio from time to time in order to teach his pupils how best to form new compositions.
Many studios would have signature styles that could be seen in the work of each and every assistant, hence the common term of "From the Studio of" when a specific attribution was not possible. Consistency was very important to Verrocchio as he would use his team of artists to complete elements of his own commissions and did not want his own reputation to be tarnished.
Whoever the artist, this sketch is one of the more beautiful items in this medium from the Renaissance and gives an insight into the workings of the famous studio of Andrea del Verrocchio during the Early Renaissance.