Some science web sites use frames which appear unappealing and cluttered. Flashy advertisements may distract your students from the science content and slow down the browser. Page acquisition time. Caching items locally or using a web harvesting application such as WebWhacker can solve time-loading problems. Many NASA sites become very busy and difficult to access when new scientific discoveries are made.
Some sites offer only a limited number of connections.
Also, accessing sites overseas can sometimes cause long wait times for web page connecting and loading. Load time is important when considering the use of a site for a classroom demonstration. The best way to be safe with a demonstration is to harvest the web site locally and view it from your computer's hard drive or another external mass-storage device. Consider your connection speed when you access a web site. Accessing large movie files with a 14.4 modem may not be worth your time unless they are extremely unique.