I am a pre-service teacher and I have seen this in many of the lower elementary classrooms. The lower elementary that I have visited have said they do not have enough time to include science in their regular school day. I sugguest that you keep incorporating science in your classroom through cross-curricular lessons. You could read a book that focuses on science during their reading time. I have seen teachers use many different techniques that includes science in other subject areas. Those teachers are just making sure that their students are receiving science time and have stressed the importance of keeping science involved in the lower elementary.