Final answer:
Lev Vygotsky would be pleased with Juan's father's approach, as it aligns with his sociocultural theory of development and the concept of scaffolding within the Zone of Proximal Development.
Step-by-step explanation:
The theorist who would be pleased with Juan's father giving him progressively less help with puzzles is Lev Vygotsky. Vygotsky's sociocultural theory of development focuses on the importance of social interactions and cultural background in learning and cognition. He proposed the concept of the Zone of Proximal Development (ZPD), where a learner can perform a task under adult guidance or with peer collaboration that they could not achieve alone. Over time, as the learner becomes more capable, the support is gradually withdrawn, a process known as scaffolding. This aligns with Juan's father giving less help as Juan becomes more skilled at puzzle solving.