Q: Will I hold back an advanced student if we train together?
A: I have often observed in my many years of training, practicing, and teaching Aikido that many beginner or inexperienced Aikido students seem to be intimidated when training with a more advanced student. At seminars and large classes, I often see less experienced students (perhaps subconsciously) pairing themselves with other less experienced students, and conversely more advanced aikidoka pairing themselves with others of the same level. This is very unfortunate, as both beginners and more advanced students can learn from each other.
A less experienced student can learn much from experiencing first-hand how more advanced students move and perform a particular technique. A more advanced student with the proper attitude should have the desire to impart his or her Aikido knowledge and help less experienced students learn and become more proficient. Hopefully every seminar, class or practice of a particular technique is a learning experience for both partners in their role of Nage or Uke.
That being said however, it is true that many more advanced Aikido students (a.k.a. Aikidoka) prefer to practice with others of the same level - especially when practicing more advanced techniques - because then they can do it faster and more advanced method. It is also probably true that many less experienced students feel more comfortable practicing with others of the same level. However, sometimes two inexperienced students trying to understand the mechanics of a technique is like a "blind-man-leading-blind-man" situation. Neither understands clearly the mechanics of the situation without more instruction from the Sensei. A good Sensei will usually overcome this propensity to pair up with others of the same level by periodically asking students to change partners.
So, getting back to the question; a less experienced student should not feel they are holding back a more advanced student by asking them to practice with them. OSensei said, "Failure is the key to success; each mistake teaches us something." He also said, "Progress comes to those who train and train..." Beginner and advanced aikidoka training together is a win-win learning situation for both.