The Navodaya Vidyalaya entrance exam for class VI and IX is completely based on the CBSE syllabus. Thus, NCERT books are appropriate for expediting the learning process and gathering all the relevant information. Besides, you may also refer to JNVST preparation guides and booklets as these mostly cover additional questions from all the important subject areas. Give attention to the MAT section. You can refer to additional MAT guides and books for scoring well in the examination.