Let me begin by applauding your desire to add more hands-on exploration and play to your kindergarten classroom. Are you part of a kindergarten team at your school? Have the kindergarten classrooms used block centers in the past? Are there any sets of blocks in storage at your school?
The notion that you are experiencing some "pushback" from your school principal when it comes to adding blocks to your classroom environment harkens me back to the words spoken by a pre-kindergarten teacher I interviewed at one urban elementary school in a large school district in Florida during my dissertation study examining the unforeseen consequences of high-stakes testing. The pre-kindergarten had formerly taught 32 years in kindergarten. She left kindergarten "in protest" because she refused to take down centers like blocks and housekeeping in favor of academic mandates like a 90-minute reading block.
A few years later, a kindergarten teacher in southeast Idaho, who was a graduate student in my early childhood courses at a local university, wanted to participate in the field-testing of the Ramps and Pathways project. I was an R&P site facilitator working with teacher participants. Her principal responded that in essence, the direct instruction models employed by the district seemed to be working (this kindergarten teacher taught as a Reading First school) and she was asked to decline the opportunity to participate.
Another teacher who formerly taught 2nd grade and was new to kindergarten the year of field-testing, participated in the R&P pilot study in Southeast Idaho. When this kindergarten teacher went to set up her centers prior to the initial R&P training workshop, she couldn't find the classroom blocks. She approached the school principal who told her that all the blocks had been placed on the "auction block" in an effort to replace developmental centers with academic centers. The school custodian learned through the grapevine that the kindergarten teacher was looking for the blocks. He brought her to a storage room where he had placed them in a garbage can for "safe keeping" and he helped her return them to the kindergarten classroom.
As you can see, your dilemma is not new or unfamiliar to many kindergarten teachers nationwide. However, the learning and developmental benefits and opportunities that can be achieved in the block center are numerous and well supported by research. All developmental domains and academic content areas can be addressed during block play, as noted extensively in the other blog responses. A block center does not take away from academic learning. Block play provides a meaningful context for academic learning as children actively use and apply mathematical thinking, scientific reasoning, engineering design, not to mention, language, cognitive, social, and fine motor skills.
Many important resources have been recommended. I would also urge you to read Miller and Almon's (2009) article, "Crisis in the kindergarten: Why children need to play in school" that was published by the Alliance for Childhood. Beth Van Meeteren, the Director at UNI's Regent's Center for Early Developmental Education has also authored a professional STEM Math Module, "Exploring Geometry through Blocks" that would be equally helpful to you. For more information on Ramps & Pathways, see Ramps and Pathways: A constructivist approach to physics with young children, published by NAEYC and STEM learning with young children: Inquiry teaching with Ramps and Pathways that is published by TCP.
To avoid being adversarial or confrontational, be sure to frame your conversation(s) with your principal using a proactive stance as much as possible. Remind your principal that you are both on the same side and you desire the same thing - that is, to maximize children's learning and development. Hopefully, your principal will not only appreciate your courage and conviction, but in the end, your principal will value and respect your knowledge and expertise with regard to using best practices to promote young children's learning and development. Utilize the many recommended resources and research available to help enlighten (and educate) your principal. Keep a running record that chronicles your conversations and overall experience. Your reflections and gained insights may serve as the substance for a published article someday!