The best option for students joining band for the first time is to start on a beginner level instrument. These instruments are designed and built to maximize the initial success of beginning musicians. Instrument manufacturers accomplish this in several ways.
For beginner instruments, manufacturers select materials that will be more durable and consistent in their response for students. This is important because as students learn to hold and care for their instruments, they will sometimes drop them or attempt to put them together incorrectly. Beginner instruments are built to withstand the rigors (and occasional abuse) that young students tend to ask of them.
Beginner instruments also use materials which will be more consistent despite changes in temperature and humidity. For example, beginner-level woodwind instruments like the clarinet will be made of an ABS resin material.
Step-up instruments use higher quality materials such as silver, gold, and grenadilla wood. These materials tend to allow musicians to play with richer, fuller tone and express a wider variety of tonal capability. Of course, when students are first beginning to play, the beginner-level instruments compensate for students' inexperience by limiting the tonal range of the instrument so students can blend together in the full band ensemble.
Beginner instruments are typically a little smaller than step-up instruments. As students grow and develop competency on their instruments, they will be able to supply a larger volume of air through the instrument, resulting in warmer, richer, fuller tone. Again, when students are first beginning music study, they tend to be smaller and therefore, the smaller instrument is more appropriate.
The bore size (diameter of the tubing) will also be larger on a step-up instrument compared with a beginner-level instrument. This also allows more air to pass through the instrument, for the same reasons as above.
Some beginner level instruments lack features that students will eventually need as they advance. These are omitted in the design of the beginner instrument for several reasons. Of course, they might be left out for the cost savings in manufacturing, but typically they are features found in more advanced playing. For example, step-up saxophones may have additional keys to allow them to play higher or lower. Step-up trombones feature an F-attachment ("trigger"), allowing the musician to use alternate positions to save energy and play faster and lower.
Step-up instruments will be manufactured using many hand-crafting processes and skills. For example, many step-up brass instrument bells are made of a single, hand-hammered piece of brass. This labor-intensive process results in an instrument that will be more resonant than the machine-spun, welded bell found on the beginner-level instrument.
The best resource for answering this question is your child's band director. If your child has been playing for several months and expresses an interest to continue through multiple grades, this is often an indication that your child may be ready for a step-up.
Another factor to keep in mind when considering a step-up instrument is your child's musical goals. If s/he wants to audition for honor bands, top-chair, or take private lessons, this is also a good indication that your child may be ready for a step-up instrument.
And of course, a reputable school band instrument retailer will be happy to walk with you through answering these questions to help determine the most appropriate and beneficial path for you and your musician.
That's a fair question. Any serious athlete will at some point develop preferences for certain brands and pieces of equipment which he/she feels benefits his/her performance in the game. A skilled driver may be competent to drive a Ferrari at high-speed, but a teenage driver would most likely be more suited to a __________(insert your favorite under-powered 4-cylinder sedan).
In the same way, advancing musicians will find themselves developing preferences and seeking better equipment to enhance the skills they are developing from practicing and performing.
Any quality school music retailer should offer several levels of step-up instruments to help fit the individual needs of each student, and affordable financing options to fit each situation.
Best wishes for your child's continued musical growth!