327J: Late 50’s/Early 60’s Long Island NY Grade School Reader

I’m looking for a book I remember so I can reconnect with the late sister I never knew.
I was born in 1965. I have one living sister (June, born: 1957) and one who passed away before I was born (Susan: born 1948).
I think the book belonged to my sister Susan, who was killed by a drunk driver in 1963. My parents couldn’t bear the pain so most of her things were not kept–too many memories. A few schoolbooks were left in the basement. I remember one especially…it could have been Susan’s or my other sister, June’s. I hope this information provides you with an idea of the time period/range of dates involved. Fairly positive it was before the mid-1960s.
The last time I saw it was a very long time ago, probably around 1973. I’ve been looking for it ever since. It was a grade school reader, blue boards…would have been used on Long Island, NY, in either Suffolk or Nassau County. I believe the first story was about boys vs. girls building a tree house. I think the girls put curtains, etc. on the windows. There are pictures throughout the book, but I don’t think the reading level was too young (not Dick and Jane, for example). There was also a story about a circus with an illustration I clearly remember of a lady in a tutu standing on the back of a running show pony.
I don’t remember much else. I think it was fairly thick, and the standard size for a hardback book.
Our address in New York was in St. James, NY, but my sister Susan only lived there for about two years. Prior to that I believe my family lived on Duffy Avenue, Hicksville, NY. This might help with the school districts.
If you could find the title for me, it would mean the world, because I could try to track down the book. When I was child I liked reading it, but I think when my mom saw it, it was either given or thrown away because it was too painful for my parents. Today the book would also be a connection to my late sister — even though it wouldn’t be her copy, it would still be something she read.
Many, many thanks. I’m sorry I can’t provide more information.