Experience
Many students lack significant life experience in terms of manual skills. How to make a graph by hand; how to use a meter stick; measuring with instruments.
Example 1: in teaching math students can calculate any unknown in similar triangles. Sent outside with a 50 meter tape to measure the height of the school, they stand around awkwardly wondering how to make real measurements to determine and unknown (and unmeasurable) height. :(
Example 2: in a test on measuring, an 8th grade student had a ruler with centimeter tick marks and numbers as well as millimeter tick marks and numbers. However, there were no words on the ruler (like "centimeter.") As a result of having no words, the student was unable to recognize which numbers were centimeters and which numbers were millimeters and therefore unsure how to use the ruler to measure. They were unable to complete any question requiring measurement with a ruler. :(
So they need a lot of lab activity and a lot of varied experiences.
Vertical Alignment
Science gets increasing abstract and content heavy as students mature. So, early MYP grades should be very rich in experience, lab work, manipulating material and measuring data. This will taper off slightly as the class becomes more content heavy in grade 9 and up. The early experience also means that later science classes do not have to teach basic experiment design all over; high school teachers can presume early experience and use time for doing labs and teaching.